Regrowth Concentration Zero (RC0) as Complementary Endpoint Parameter to Evaluate Compound Candidates During Preclinical Drug Development for Cancer Treatment

The screening process for potential anticancer drugs involves expensive and time consuming preclinical and clinical trials (CT) before a drug is approved for clinical use (CU). At present, there is a “bottleneck” at the CT/CU transition because many drugs that showed promising results during preclinical research did not pass clinical trials. We speculated that the endpoint parameters (the inhibitory concentration 50 (IC50) or lethal concentration 100 (CL100)) commonly used in proliferation assays for short-term periods (24-72 h) are not useful to predict the antiproliferative effect in vivo, especially during clinical trials. We propose the use of a parameter, regrowth concentration 0 (RC0), which will define the concentration and time necessary to kill 100 % of the cells and prevent regrowth when drug is removed. The RC0 might introduce a new bottleneck at the preclinical stage, “preclinical bottleneck”, that will select for drugs with more chances to pass clinical trials and improve the success rate of anticancer screening programs. Our proposal is supported by experiments done with the DBTRG-05MG human glioma cell lines exposed to short and long-term incubation with three different DNA replication inhibitors (aphidicolin, hydroxyurea and etoposide) and retrospective analysis of clinical trials for these drugs.